Magnetic micropositioner and method of providing the same

ABSTRACT

A micropositioner is provided, which contains an outer magnetic pole-piece and an inner magnetic pole-piece located within the outer magnetic pole piece. At least one permanent magnet is located between the inner magnetic pole piece and the outer magnetic pole-piece. At least one coil is located between the inner magnetic pole-piece and the outer magnetic pole-piece, wherein the at least one coil is capable of directing magnetic flux between the inner magnetic pole-piece and the outer magnetic pole-piece. An outer movable shell is also movably connected to the outer magnetic pole-piece.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 10/858,482, filed on Jun. 1, 2004, which is acontinuation-in-part of U.S. patent application Ser. No. 10/448,336,filed May 29, 2003, which claims the benefit of U.S. ProvisionalApplication No. 60/383,956, filed on May 29, 2002. The entire contentsof the above applications are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention is generally related to micropositioners, and moreparticularly is related to a micropositioner having multiple degrees offreedom.

BACKGROUND OF THE INVENTION

A fast tool servo is a well-known device that can be added to a new orexisting machine tool to provide an additional axis of motion betweenthe cutting tool and a workpiece. A fast tool servo most notablydistinguishes itself by its ability to move the tool at a much higherbandwidth, that is at a high speed of controlled, repetitive motion, onits axis relative to the other machine tool axes, with accuracy equal toor better than that of the other tool axes. Fast tool servos fall intotwo broad categories: rotary and linear. A rotary fast tool servoproduces relative motion between the cutting tool and a workpiece byrotation of a swing arm that carries the tool at a fixed radius from theaxis of rotation. A linear fast tool servo produces relative motionbetween the cutting tool and a workpiece by producing a lineartranslation of the tool.

A rotary fast tool servo is preferred in certain precision machiningapplications that are intolerant to the reaction force developed by alinear fast tool servo. For instance, in an application where it isdesired to produce a textured surface on a spherical-shaped workpiece afast tool servo is mounted on a rotary table that allows the tool toengage the workpiece, which is mounted to a spindle, at all points fromits “pole” to its “equator”. A rotary-type mechanism oriented with itsrotation axis parallel to the rotary table generates a reaction torqueon the rotary table, which can be allowed to float as a reaction mass orbe locked and allowed to transmit the torque to the machine structure.In the later case the machine structure experiences a disturbance torquewhose value does not depend on the angle of the rotary table. Incontrast, a linear fast tool servo generates a reaction force on therotary table. This is generally not a problem when the rotary table ispositioned so that the reaction force is parallel to the direction oftravel of the slide carrying the rotary table. However, when the rotarytable is positioned so that a component of the reaction force isperpendicular to the direction of travel of that slide, that forcecomponent is transmitted by the slide to the machine structure as adisturbance. To the extent that the tool/workpiece interaction isaffected by disturbances to the machine structure, a linear fast toolservo will produce errors in the desired surface texture as a functionof “latitude” on a spherical workpiece.

Current fast tool servo technology does not support sufficient bandwidthto meet certain manufacturing goals and is also not sufficiently fast tomachine certain types of materials, for example, some plastics,properly. It is desirable to have a method and apparatus for a rotaryfast tool servo having a higher bandwidth than currently availablesystems.

Thus, a heretofore unaddressed need exists in the industry to addressthe aforementioned deficiencies and inadequacies.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide a micropositioner. Themicropositioner contains an outer magnetic pole-piece and an innermagnetic pole-piece located within the outer magnetic pole piece. Atleast one permanent magnet is located between the inner magnetic polepiece and the outer magnetic pole-piece. At least one coil is locatedbetween the inner magnetic pole-piece and the outer magnetic pole-piece,wherein the at least one coil is capable of directing magnetic fluxbetween the inner magnetic pole-piece and the outer magnetic pole-piece.An outer movable shell is also movably connected to the outer magneticpole-piece.

Other systems, methods, features, and advantages of the presentinvention will be or become apparent to one with skill in the art uponexamination of the following drawings and detailed description. It isintended that all such additional systems, methods, features, andadvantages be included within this description, be within the scope ofthe present invention, and be protected by the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the invention can be better understood with reference tothe following drawings. The components in the drawings are notnecessarily to scale, emphasis instead being placed upon clearlyillustrating the principles of the present invention. Moreover, in thedrawings, like reference numerals designate corresponding partsthroughout the several views.

FIG. 1 is an isometric projection of the rotary fast tool servo assemblyin accordance with a preferred embodiment of the present invention.

FIG. 2A is an isometric projection of a cutting tool according toprinciples of the preferred embodiment of the present invention.

FIG. 2B is a top view of the cutting tool of FIG. 2A in accordance witha preferred embodiment of the present invention.

FIG. 2C illustrates an enlargement of the cutting tool cutting edge inaccordance with a preferred embodiment of the present invention.

FIG. 3 is an isometric projection of an alternative embodiment of thecutting tool of FIG. 2A.

FIG. 4 is a side view sketch of a swing arm assembly of FIG. 1.

FIG. 5 is a front view sketch of the swing arm assembly of FIG. 4.

FIG. 6 is an isometric projection of a tool clamp flexure of the swingarm assembly of FIG. 4.

FIG. 7 is a side cross-sectional view of the swing arm assembly of FIG.4.

FIG. 8 is an isometric projection of a pair of flexures of the swing armassembly of FIG. 4.

FIG. 9 is an isometric projection of the swing arm assembly of FIG. 4illustrating two pairs of flexure

of FIG. 8 and a workpiece in accordance with a preferred embodiment ofthe present invention.

FIG. 10 is an isometric projection of the swing arm base of FIG. 1.

FIG. 11 is an isometric projection of the swing arm assembly of FIG. 4with two pairs of flexures of FIG. 8, a workpiece, and chip shields inaccordance with a preferred embodiment of the present invention.

FIG. 12 is a perspective view of the upper chip shield of FIG. 11.

FIG. 13 is a perspective view of the lower chip shield of FIG. 11.

FIG. 14 is a perspective view of the swing arm assembly of FIG. 4 withhard stops.

FIG. 15 is a perspective view of a differential screw assembly inaccordance with a preferred embodiment of the present invention.

FIG. 16A is a top view of the differential screw assembly of FIG. 15.

FIG. 16B is a cross-sectional view of the differential screw assemblytaken along the line 16B-16B of FIG. 16A.

FIG. 17 is a perspective view of the rotary fast tool servo assembly ofFIG. 1 without the actuator.

FIG. 18 is a side view of a workpiece on a spindle of a lathe with arotary fast tool servo of an alternative embodiment on a rotary baseaccording to the invention.

FIG. 19 is a view of a workpiece on a spindle with a rotary fast toolservo on a rotary base in accorda

with a preferred embodiment of the present invention.

FIG. 20 is a skewed view of a rotary fast tool servo with a workpiece ona workpiece holder in accordance with a preferred embodiment of thepresent invention.

FIG. 21 is a perspective view of a swing arm with a damper plate inaccordance with a preferred embodiment of the present invention.

FIG. 22 is a sectional view of the swing arm with a cutting tool andretention mechanism in accordan

with a preferred embodiment of the present invention.

FIG. 23 is a rear view of the swing arm showing the tool clamp flexureof the retention mechanism in accordance with a preferred embodiment ofthe present invention.

FIG. 24 is a front view of the swing arm showing a clamp mechanism forthe pair of flexures in accordance with a preferred embodiment of thepresent invention.

FIG. 25 is a perspective view of the base of the rotary fast tool inaccordance with a preferred embodiment of the present invention.

FIG. 26 is a back bottom perspective view of the swing arm with flexureblades, a tensioning device, and sensors in accordance with a preferredembodiment of the present invention.

FIG. 27 is a side perspective view of the base with the swing arm inaccordance with a preferred embodiment of the present invention.

FIG. 28 is a side perspective view of the rotary fast tool servo systemshowing an actuator connected the swing arm in accordance with apreferred embodiment of the present invention.

FIG. 29 is a side perspective view of the rotary fast tool servo showingan enclosure encircling the actuator and a side stiffener on the base inaccordance with a preferred embodiment of the present invention.

FIG. 30 is a front view of an exemplary workpiece in accordance with apreferred embodiment of the present invention.

FIG. 31 is a schematic of a control system in accordance with apreferred embodiment of the present invention.

FIG. 32A is a perspective view of a lathe with a workpiece and anauxiliary rotary table without the fast tool servo in accordance with apreferred embodiment of the present invention.

FIGS. 32B and 32C are views illustrating a lathe with a workpiece and arotary tool servo system in accordance with a preferred embodiment ofthe present invention.

FIGS. 33A and 33B are schematic diagrams of a variable reluctanceactuator and swing arm assembly accordance with a preferred embodimentof the present invention.

FIG. 34 illustrates an embodiment of a variable reluctance actuator.

FIGS. 35A and 35B illustrate a variable reluctance actuator for use infast tool servo applications.

FIGS. 36A and 36B illustrate the armature and stator, respectively, ofthe actuator in FIGS. 35A and 35B.

FIG. 37 illustrates an embodiment of a fast tool servo having thearmature and stator supported on flexures.

FIGS. 38A and 38B illustrate a permanent magnet biased actuator forproducing linear motion and rotary motion, respectively.

FIGS. 39A and 39B illustrate a two coil and four coil current biasedactuator, respectively, for product

linear motion and rotary motion.

FIG. 40 illustrates the relationship excess acceleration forces andreaction forces in the fast tool servo

system.

FIG. 41 illustrates relative motions associated with oil damping means.

FIG. 42 illustrates an embodiment of a Hall cell.

FIG. 43 illustrates an embodiment of an actuator derived from a Hallcell.

FIGS. 44A, 44B and 44C illustrate a top view, a side view and a faceview of the actuator shown in FIG.

43.

FIGS. 45A and 45B illustrate embodiments of an actuator employing biasflux to provide preload forc

for pressurized air or oil hydrostatic bearings.

FIGS. 46A and 46B illustrate embodiments of rotational fast tool servoshaving a horizontal axis of motion (FIG. 46A) or a vertical axis ofrotation (FIG. 46B).

FIGS. 47A and 47B illustrate a radial configuration of flux-biased coilsused in conjunction with rotational fast tool servos.

FIG. 48 illustrates an embodiment of a core having a wedge shape, whichcan be used in embodiments of the invention.

FIG. 49 illustrates a micropositioner in accordance with an alternativeembodiment of the present invention.

FIG. 50 is a cross-sectional view of the micropositioner of FIG. 49.

FIG. 51 is a schematic diagram illustrating coil and magnetic flux pathsof the micropositioner of FIG. 49.

FIG. 52 better illustrates positioning of rubber bearings within themicropositioner of FIG. 49.

FIG. 53 is a schematic diagram further illustrating positioning ofrubber bearings in the micropositioner of FIG. 49, and degrees offreedom.

FIG. 54A is a cross-sectional side view of an alternativemicropositioner where an outer movable shell is suspended on a series ofstacked o-rings with bulging interference.

FIG. 54B is a cross-sectional side view of an alternativemicropositioner where an outer movable shell is suspended on a series ofstacked o-rings without bulging interference.

FIG. 55 is a schematic diagram illustrating an example of the use ofmetal flexures instead of rubber bearings.

FIG. 56A is a schematic diagram further illustrating a metal flexurebefore flexure.

FIG. 56B is a schematic diagram further illustrating a metal flexureafter flexure.

FIG. 57 is a schematic diagram further illustrating the micropositionerof FIG. 49 having integral capacitive position sensing devices.

FIG. 58 is a cross-sectional side view of a micropositioner having twodegrees of freedom, namely, the X-axis and the Y-axis.

FIG. 59 is a cross-sectional side view of the micropositioner of FIG. 58slightly modified by lacking a rubber bearing sheet near a center stage.

FIG. 60 is a top view of the micropositioners of FIG. 58 and FIG. 59.

FIG. 61 is a cross-sectional side view of a micropositioner, inaccordance with another alternative embodiment of the invention.

FIG. 62 is a cross-sectional side view of magnetic portions within amicropositioner, in accordance with an alternative embodiment of theinvention.

FIG. 63 is a cross-sectional view of the micropositioner of FIG. 62.

FIG. 64 is a cross-sectional side view of magnetic portions within amicropositioner, in accordance with an alternative embodiment of theinvention.

FIG. 65 is a cross-sectional view of the micropositioner of FIG. 64.

FIG. 66 is a schematic diagram illustrating a system having multiplemicropositioners and three degrees of freedom.

FIG. 67 is a schematic diagram illustrating a second system havingmultiple micropositioners and three degrees of freedom.

DETAILED DESCRIPTION

Referring to the drawings in detail, a high bandwidth rotary fast toolservo system is illustrated in accordance with a preferred embodiment ofthe present invention designated generally as 40. In a preferredembodiment, the high bandwidth rotary fast tool servo provides toolmotion in a direction nominally parallel the surface-normal of aworkpiece at the point of contact between the cutting tool andworkpiece.

FIG. 1 shows the high bandwidth rotary fast tool servo 40 having a swingarm assembly 42 holding a cutting tool 44 to machine a workpiece 50. Thecutting tool 44 is offset from the axis of rotation 46, as best seen inFIG. 5, of the swing arm assembly 42. The workpiece 50 is held typicallyby a workpiece holder 51 t

attaches to a lathe spindle at surface 52. The swing arm assembly 42 issupported in a base 48 having an upp

portion 60 and a lower portion 62. The upper portion 60 and lowerportion 62 are connected by a flexure hing

64. The upper portion 60 of the base 48 has a differential screwassembly 66. An actuator 68 is connected to top of the swing armassembly 42.

In operation, the actuator 68 rotates the swing arm assembly 42 suchthat the cutting tool 44 is moved into and away from the lathe-mounted,rotating workpiece 50 in a rapid and controlled manner in order tomachine the workpiece. In an alternative embodiment the swing armassembly 42 and the moving member c

the actuator 68 are integrated and are one and the same and carry thecutting tool 44. The differential screw assembly 66 together with theflexure hinge 64 provide accurate cutting tool positioning in adirection nominally tangent to the surface-normal of a workpiece at thepoint of contact between the cutting tool and workpiece and nominallyparallel to the axis of rotation of the swing arm assembly by enablingthe upper portion 60 of the base 48 to be repositioned in a fine-grainedmanner with respect to the lower portion 62 of t

base 48.

FIG. 2A shows a first embodiment of the cutting tool according toprinciples of the present invention. The cutting too 144 has a threadedhole 70, a cutting edge 72, a right/left plane of symmetry 74 thatdivides the tool into right and left halves, a left first mating surface76 and a left second mating surface 78, a right first mating surface 80and a right second mating surface 82, a top surface 84, and a backsurface 86. The left first and second mating surfaces 76 and 78 and theright first and second mating surfaces 80 and 82 form a taper angle 88bisected by the right/left plane of symmetry 74. The left first andsecond mating surfaces 76 and 78 and the right first and second matingsurfaces 80 and 82 mate with the swing arm 102 of the swing arm assembly42 as described hereinafter with respect to FIG. 5. The threaded hole 70is substantially parallel to and nominally centered on the plane ofsymmetry 74.

In one preferred embodiment, the cutting edge 72 is a diamond.Alternatives for the cutting edge 72 c

be various materials including cubic boron nitride, tungsten carbide,high speed steel, and other materials us

for precision machining metals, plastics, ceramics, glasses and foams.

FIG. 2B is a top view of the cutting tool 44 of FIG. 2A in accordancewith a preferred embodiment of the present invention. An enlargement ofthe cutting edge 72 is shown in FIG. 2C. A center point 98 on thecutting edge 72 lies in the plane of symmetry 74 of the cutting tool 44as best seen in FIG. 2C. The cutting to edge 72 has a radius ofcurvature 100 that lies in a plane that is substantially perpendicularto the plane of symmetry 74 of the cutting tool 44 and nominally in theplane of the top surface 84 of the cutting tool. In alternativeembodiments the plane containing the radius of curvature can form asubstantial angle with the to

surface 84 of the cutting tool.

FIG. 3 shows an alternative embodiment of the cutting tool of FIG. 2A.The cutting tool 90, instead of being a single piece, has a cuttingportion 92 set into a holder 94. The cutting portion 92 has a cuttingedge 9

The holder 94 has left and right first and second mating surfaces 76,78, 80 and 82 to mate with the swing arm assembly 42 as seen in FIG. 4.The holder 94 also has the threaded hole 70 substantially parallel toand nominally centered on the plane of symmetry 74.

In an alternative embodiment of the cutting tool, the cutting portion 92is bonded directly to the swing arm 102 shown in FIG. 4, without the useof a holder 94. Bonding methods include, but are not limited to,epoxying, braising, soldering and diffusion bonding.

FIG. 4 is a left side view of the swing arm assembly 42 illustrated inFIG. 1. The swing arm assembly has a swing arm 102, a tool clamp flexure104, an upper pair of flexure blades 106, and a lower pair of flexures

blades 108. The flexure blades are referred to herein as flexures andare pliant, extending members. The upper pair of flexures 106 and thelower pair of flexures 108 constrain the swing arm 102 in all degrees offreedom except rotation around an axis of rotation 46 that is nominallycoincident with the long axis of the swing arm 102. In other preferredembodiments, the axis of rotation may be offset from but substantiallyparallel to the long axis of the swing arm. The swing arm 102 has anupper hub 110 and a lower hub 112. The swing arm has a workpiececlearance cut 114 that is nominally midway between the upper hub 110 andthe lower hub 1

The clearance cut 114 extends from a front face 116 of the swing arm 102through the axis of rotation 46 and slightly beyond. A front/back plane118 extends through the axis of rotation and parallel to the front face

11 The swing arm 102 has a back clearance surface 120 that is parallelto and spaced from the front/back plane 118. The clearance cut 114allows the cutting tool edge 72 or 96 and a small portion of the cuttingtool 44 or to protrude from the back clearance surface 120 of the swingarm 102, and allows a workpiece to extend into the swing arm 102 as muchas practicable.

In an alternative embodiment, one set of three flexures are attached tothe swing arm and extend radia

from the swing arm. The three flexures support the rotatable swing armin the base and establish an axis of rotation for the swing arm. Thoseskilled in the art can appreciate that an embodiment of the presentinvention using two sets of flexures spaced apart on the swing arm sothat the cutting tool is between the two sets, provides the swing armwith structural support at two opposite ends. In contrast, a single setof flexures at o

one end of the swing arm provides a structural support that is lessrigid. Decreasing the number of flexures from four to three also reducesthe stiffness of the tool relative to the base. Preferred embodimentsinclude a trade-off analysis to determine the number of flexures used.The trade-off in choosing three, four or more flexures and one or twosets of flexures involves considering the reduction of stiffness versusthe reduction in moving mass and increase in the work space volumearound the tool. To maintain a constant stiffness level a

the tool, reducing the number of flexures requires increasing theirdimension or choosing a material with a higher stiffness. Reducing thenumber of sets from two sets to one set of flexures (for example, byremoving the lower flexures 108) requires the same trade-off analysis,increasing the bending stiffness of the swing arm

and possibly decreasing the length of the flexures. The material of theflexures can include, without limitation steel, beryllium-based alloysand materials that have a high fatigue strength to stiffness ratio. Thematerial of the swing arm can include, without limitation, aluminum,steel, beryllium and composite materials that have high stiffness toweight ratio.

The central portion of the upper flexure blade pair 106 is fixed to theswing arm 102 by bonding the flexure blades in a pair of upper slots 122in the upper hub 110, and can be further secured by tightening aplurality of upper slot screws 124. The central portion of the lowerflexure blade pair 108 is fixed to the swing arm 102 by bonding theflexure blades in a pair of lower slots 126 in the lower hub 112, andcan be further secured by tightening a plurality of lower slot screws128. A tool clamp screw 132 carried by the swing arm 102 works with thetool clamp flexure 104 to fix the cutting tool 44 or 90 in the swing arm102.

FIG. 5 is a front view of the swing arm assembly 42 of FIG. 4 holdingthe cutting tool 90 of FIG. 3. The swing arm 102 has a right/left planeof symmetry 136 that contains the swing arm axis of rotation 46 and isperpendicular to the front/back plane 118, shown in FIG. 4. The swingarm 102 has a slot 138 that receives t

cutting tool 90. The slot 138 has a plane of symmetry 140 that dividesthe slot 138 into right and left halves. The slot 138 is located in theswing arm 102 approximately midway between the upper hub 110 and thelower hub 112. The slot plane of symmetry 140 is parallel to theright/left plane of symmetry 136 and is offset from the swing arm axisof rotation 46 by a distance equal to an offset radius 142.

The cutting tool 90 is located in the swing arm 102 by mating foursurfaces 76, 78, 80 and 82 on the cutting tool 90, which form a taperangle 88, to a pair of surfaces 144 and 146 in the swing arm slot 138,and mating the back surface 86 of the cutting tool 90 with a pair ofback blades 148 and 150 as shown in FIG. 6

the tool clamp flexure 104.

It can be appreciated by those skilled in the art that the holding forceand alignment between a tool

ar tool holder can be improved by providing the tool with a taper anglethat mates with a receiving feature in a

t holder. The present embodiment improves upon this method by creatingfour mating areas on the tool for contact between the tool and the slot.Those skilled in the art will recognize that the discontinuity of the

mati surface 76 and 78 and of the mating surface 80 and 82 by the recessin between the two portions provides

fo distinct areas of contact between the cutting tool 90 and thereceiving surfaces 144 and 146 of the swing arm slot 138. This resultsin improved mating and alignment of the cutting tool 90 with the swingarm slot 138, compared to a design that utilizes simpler continuoussurfaces on the cutting tool 90.

When the cutting tool 90 is held in the swing arm 102, the cutting toolplane of symmetry 74 and the swing arm slot 138 plane of symmetry 140are coincident, and the cutting tool top surface 84 is nominallyperpendicular to the swing arm axis of rotation 46. Furthermore, thecenter point 98 on the cutting tool edge is offset from the swing armright/left plane of symmetry 136 by a distance equal to the offsetradius 142, and the center point 98 lies nominally in the swing armfront/back plane 118, as seen in FIG. 4. In alternative embodiments thecenter point 98 lies in front of or behind the swing arm front/backplane 118.

FIG. 6 shows the tool clamp flexure 104. The tool clamp flexure 104 hasa front blade 152 that is interposed between the first back blade 148and the second back blade 150 and is substantially perpendicular theback blades 148 and 150. The tool clamp flexure 104 has a hole 154 forreceiving a fastener 156 to

secur the tool clamp flexure 104 to the swing arm back surface 158 asseen in FIG. 4. The tool clamp flexure 104

a has an access slot 160. The access slot 160 allows access to the toolclamp screw 132.

FIG. 7 is a side cross-sectional view of the swing arm assembly 42. Inoperation, the tool clamp flexure

104 is located on the swing arm 102 such that the cutting tool 90 islocated under the front blade 152 of the

t clamp flexure 104. The tool clamp screw 132 which is accessiblethrough the flexure slot 160, pushes on the front blade 152 of the toolclamp flexure 104 causing the front blade 152 to deflect and contact thecutting to top surface 84, forcing the cutting tool 90 downward in theswing arm slot 138. In an alternative embodiment screw engages thethreaded hole 70 in the cutting tool 90 to draw down the cutting tool 90into the swing arm slot 138.

When the cutting tool edge 96 and workpiece 50 contact each other duringuse, a cutting force 164

an thrust force 166 develops between the two bodies. The cutting force164 is in a direction substantially

paralle the swing arm axis of rotation 46. The thrust force 166 is in adirection substantially perpendicular to the

sw arm axis of rotation 46. Both the cutting force 164 and the thrustforce 166 lie substantially in the plane of symmetry 140 of the slot 138shown in FIG. 5. The cutting force 164 and thrust force 166 are opposedby the upper pair of flexure blades 106 and the lower pair of flexureblades 108, as seen in FIG. 5. Still referring to FIG. 7, the thrustforce 166, in this example, also produces a torque 168 by acting at adistance equal to the

o set radius 142 from the swing arm axis of rotation 46. The torque 168is opposed by a torque produced by the actuator 68 as shown in FIG. 1.

FIG. 8 shows the pair of upper flexure blades 106. The lower flexureblades 108 are similarly constructed in this embodiment. Each pair offlexure blades 106 and 108 has a first flexure blade and a secondflexure blade positioned substantially perpendicular to each other. Eachof the blades 106 has a plurality of holes 172 and 174. The outer holes174 are used for securing the flexure blades 106 to the swing arm base48. The inner holes 172 allow for the upper slot screws 124 to pass fromone portion of the upper hub 110 to another portion of the hub forsecuring the flexure blades 106 in the slots 122. The hole in theflexure blade through which the screw passes provides adequate clearanceso there is no interference with the tension.

FIG. 9 shows the swing arm assembly 42 and the workpiece 50. The swingarm assembly 42 has the upper pair of flexures or flexure blades 106 inthe upper hub 110 and the lower pair of flexures or flexure

blades 108 in the lower hub 112. In the swing arm assembly 42, the upperand lower pairs of flexure blades or elements 106 and 108 are orientedat an angle of forty-five degrees from the swing arm right/left plane ofsymmetry 136, as shown in FIG. 5, so as to maximize the open spacebetween the workpiece 50 and the swing arm base 48, as best seen in FIG.1.

The central portion of the pair of the upper flexure blades 106 is fixedto the swing arm 102 by

bondi the flexure blades 106 in the upper slots 122 in the upper hub110, and can be further secured by tightening

t upper slot screws 124. The upper slot screws 124 pass through holes172 of the upper flexure blades 106. The central portion of the pair ofthe lower flexure blades 108 is fixed to the swing arm 102 by bondingthe flexure blades in the lower slots 126 in the lower hub 112, and canbe further secured by tightening the lower slot screws 128. Thoseskilled in the art will recognize that by properly tightening the screws124 and 128, the bonded joint can be preloaded in compression to theextent necessary to avoid stress reversal in the bonded

jo during use of the embodiments of the present invention. It is wellknown that stress reversal and tension/compression cycles, reduce thefatigue life of a mechanical component.

Rotation of the swing arm 102 relative to the base 48 causes anout-of-plane bending in the upper and lower pairs of flexure blades 106and 108. The in-plane stiffness of each flexure blade, when combined asa system of upper and lower pairs of flexure blades 106 and 108,constrains the swing arm 102 in five of six possible degrees of freedom,leaving free rotation around the swing arm axis of rotation 46 shown inFIG. 5. That is, the upper pair of flexure blades 106 and lower pair offlexure blades 108 support and constrain the swing arm 102 as afixed-end/fixed-end beam with a single degree of freedom of rotationaround the swing arm axis of rotation 46. Those skilled in the art willrecognize that the swing arm 102 is actually over-constrained by theupper and lower pairs of flexure blades 106 and 108 in the sense thatthe blades will resist large rotations that would require them tostretch substantially. This is acceptable in the embodiments of thepresent invention since the swing arm 102 is subjected to relativelysmall rotation angles around the swing and axis of rotation 46. Sincethe cutting edge 96 is located inside of the virtual cylinder formed byjoining the upper hub 110 and lower hub 112, and is spaced a smalldistance (i.e., the offset radius 142) from the swing

a axis of rotation 46, the bending moment on the swing arm 102 from thecutting force 164 as represented by

1 in FIG. 5, is kept within a tolerable range. In an alternate preferredembodiment, the cutting edge 96 is located outside of the virtualcylinder formed by joining the upper hub 110 and lower hub 112, and isspaced a larger distance (i.e., the offset radius 142) from the swingarm axis of rotation 46.

One skilled in the art will recognize that the swing arm 102 and flexureblades 106 and 108 can be manufactured as a single unit by machining asingle piece of material using a variety of methods including

w electro-discharge machining, and will also recognize that the swingarm 102, flexure blades 106 and 108, and portion or all of the base 48can be manufactured as a single unit by machining a single piece ofmaterial with the above described methods.

As described hereinbefore, preferred embodiments can include as aminimum, one set of three flexure

that are disposed on the swing arm and extend radially from the swingarm. The blades are disposed around swing arm in an angular relationshipas illustrated in FIG. 9 of angle α or β between the blades. The anglesα and β can be optimized such that the flexures keep the center line ofthe rotating piece fixed. In an embodiment, the three flexures form aT-shape wherein angles α=β=90°. In another preferred embodiment theangles α and β are non-equidistant but are optimized to increase thework space around the tool while providing the desired amount of supportand stiffness at the tool to resist the cutting forces developed betweenthe tool and the workpiece.

The swing arm base 48 is shown in FIG. 10 in accordance with a preferredembodiment of the present invention. The outer ends of the pair of theupper flexure blades 106 are fixed to the swing arm base 48 by bondingthe flexure blades 106 in a plurality of base upper slots 176, and canbe further secured by tightening a plurality of base upper slot screws178. The outer ends of the pair of the lower flexure blades 108 arefixed to the swing arm base 48 by bonding the flexure blades in aplurality of base lower slots 180, and can be further secured bytightening the base lower slot screws 182. Those skilled in the art willrecognize that by properly tightening the screws 178 and 182 the bondedjoint can be preloaded in compression to the extent necessary to avoidstress reversal in the bonded joint during use of the invention. It iswell known that stress reversal, tension/compression cycles, reduces thefatigue life of a mechanical component.

The upper and lower pairs of flexure blades 106 and 108 as seen in FIG.9, are preloaded into tension during assembly of the flexure blade pairswith the swing arm 102 and the swing arm base 48. Those skilled the artwill recognize that the performance of the flexure blades is improved byhaving a certain amount of preload tension in the blades during use. Theswing arm 102 and the swing arm base 48 are made of material that have asimilar coefficient of thermal expansion (CTE-1). The upper and lowerpairs of flexure blades

10 and 108 are made of a material that has a higher coefficient ofthermal expansion (CTE-2). In an embodiment the swing arm 102 and swingarm base 48 are made of steel, and beryllium-copper is used for thepairs of flexure blades 106 and 108, resulting in a difference incoefficient of thermal expansion of approximately 3 parts per millionper degree Fahrenheit. Initial assembly of the upper and lower pairs offlexure blades 106

and 108 with the swing arm 102 and the swing arm base 48 is performed atthe ambient temperature that the fast tool servo will be used at, and isnominally room temperature. The upper and lower pairs of flexure blades

1 and 108 are bonded to the swing arm 102 and swing arm base 48 at atemperature above the ambient use temperature. The choice of temperatureduring the bonding process depends on the materials chosen for the swingarm 102, base 48, and the pairs of flexure blades 106 and 108, and thedesired level of tension preload the flexure blades. These parameterscan be chosen to allow a bonding temperature in the range of the

ambie temperature that the fast tool servo will be used to many hundredsof degrees Fahrenheit, thus accommodating bonding methods ranging fromelevated temperature-cure adhesives to soldering and brazing. Because

CTE is greater than CTE-1, a tensile force is developed in the upper andlower pairs of flexure blades 106 and 108 when the temperature of thebonded assembly is returned to the ambient use temperature.

Still referring to FIG. 10, the flexure hinge 64 is shown between theupper portion 60 of the base 48

a the lower portion 62 of the base 48. As indicated with respect to FIG.1, the differential screw assembly 66

h a tip 214, as shown in FIG. 1, that is carried by a block assembly 184in the upper portion 60 and engages the lower portion 62 of the base 48.The rotation of the screw 66 is used in a method of adjusting theposition of the cutting edge relative to the workpiece. Further, boththe plurality of base upper slots 176 and the plurality base lower slots180 are located on the upper portion 60 of the base 48.

FIG. 11 shows the swing arm assembly 42 with the workpiece 50. The swingarm assembly 42 has

an upper chip shield 188 and a lower chip shield 190 that protects theflexure blades 106 and 108 set in the upper hub 110 and lower hub 112 ofthe swing arm assembly 42 when the swing arm assembly 42 is secured tothe base 48 as shown in FIG. 1. The upper chip shield 188 also shown inFIG. 12, is mounted below the upper flexure blades 106. The lower chipshield 190 also shown in FIG. 13, is mounted above the lower flexureblades

108.

The swing arm 102 has an upper skirt 192, as best shown in FIG. 9, and alower skirt 194 to prevent debris generated during use from entering andaccumulating between the swing arm 102 and the base 48 in the

areas near the upper and lower pairs of flexure blades 106 and 108. Theupper chip shield 188 mounts to the swing arm base 48 and engages theupper skirt 192 to form a simple labyrinth seal above the upper skirt192. The lower chip shield 190 mounts to the swing arm base 48 andengages the lower skirt 194 to form a simple labyrinth seal below thelower skirt 194.

The upper chip shield 188 is formed of two pieces. One of the pieces isshown in FIG. 12 and has a

li 196 that forms an annular groove 198 that receives the upper skirt192 of the swing arm 102. In addition, the upper chip shield 188 has atapered edge 200 on the front portion to increase the clearance for theworkpiece and the workpiece holder 51. The upper chip shield 188 has aplurality of vertical holes 202 for receiving fasteners to secure theupper chip shield 188 to the base 48. In addition, the upper chip shield188 has a plurality of horizontal holes 204 through which the hard stops212 as seen in FIG. 14 extend.

The lower chip shield 190 is formed of two identical pieces. One of thepieces is shown in FIG. 13. The lower chip shield 190 has a plurality ofholes 210 for receiving fasteners to secure the lower chip shield 190

t the base 48.

FIG. 14 shows the swing arm assembly 42 with four hard stops 212. Thehard stops 212 are located near the swing arm 102 below the upper skirt192 and extend outward from the swing arm 102 substantiallyperpendicular to the swing arm right/left plane of symmetry 136. Theupper chip shield 188, as seen in FIG. 12, has a thickened cross-sectionto accept the hard-stops 212. A small gap 213 between an end of eachhard stop 212 and the swing arm 102 allows normal rotation of the swingarm. The hard stops 212 act in pairs to limit the rotation angle of theswing arm 102 to prevent damage to the upper and lower pairs of flexureblades 106 and 108. Excessive rotation of the swing arm 102 causesclosure of a pair of gaps 213 that limits rotation of the swing arm.

FIG. 15 is a perspective view of the differential screw assembly 66. Thedifferential screw assembly

has a tip 214, a coarse adjustment screw 216, a fine adjustment screw218, and a housing 219. The interface between the tip 214 and the fineadjustment screw 218 consists of a set of machined threads having athread pitch P-1. The interface between the fine adjustment screw 218and the housing 219 consists of a set of machined threads having athread pitch P-2. In operation, the differential screw assembly 66 ismounted in the upper portion 60 of the swing arm base 48 with the tip214 in contact with the lower portion 62 of the swing arm base 48.

FIG. 16A is a top view of the differential screw assembly 66. FIG. 16Bis a side cross-sectional view

the differential screw assembly 66 taken along the line 16B-16B of FIG.16A. The extension of the tip 214

on the differential screw 66 is adjusted using the coarse adjustmentscrew 216 and the fine adjustment screw 218 Turning the coarseadjustment screw 216 transmits rotation through pin 220 to the tip 214while the fine adjustment screw 218 is stationary. Locking the coarseadjustment screw 216 and rotating the fine adjustment screw 218 causesmotion in one direction between the coarse adjustment screw 216 and fineadjustment screw 218, and motion in the opposite direction between thefine adjustment screw 218 and the housing 219, while pin 220 preventsrotation of the tip 214. The motion of the tip 214 relative to thehousing 219 is related to the difference in the thread pitches P-1 andP-2.

FIG. 17 shows the rotary fast tool servo assembly 40 without theactuator 68. The workpiece 50 is

al shown. The swing arm assembly 42 is mounted in the upper portion 60of the base 48. The base 48 has a

pai essentially concentric circular openings 222 to receive the swingarm assembly 42. Each of the two openings 222 has the plurality of slots176 and 180 to receive the flexure blades extending radially from theswing arm 42.

The differential screw assembly 66 is mounted in the upper portion 60 ofthe base 48. The upper

port 60 of the base 48 is joined to lower portion 62 of the base 48 bythe flexure hinge 64. The flexure hinge 64 extends across the swing armbase from the left side of the base 48 to the right such that flexing ofthe flexure hinge 64 causes up/down repositioning of the cutting tool90. By rotating the upper portion 60 of the base 48 about the flexurehinge 64, the cutting tool is adjusted vertically relative to theworkpiece using the differential screw assembly 66. The lower portion 62provides a surface 226 for the tip 214 of the differential screwassembly 66 to contact. The lower portion 62 has a mounting surface 228for attaching the rotary fast tool

se assembly 40 to a machine tool 240, as seen in FIG. 18.

A preload spring maintains contact between the tip 214 of thedifferential screw assembly 66 and the surface 226 of the lower base 62.Adjustments of the coarse adjustment screw and fine adjustment screw

cau the tip 214 to bear against the surface 226 of the lower base 62causing a rotation of the upper portion 60 of

t swing arm base 48 around an axis that is parallel to the long axis ofthe flexure hinge 64 and substantially at

center of the flexure hinge. This rotation of the upper portion 60 ofthe swing arm base 48 causes the cutting tool edge 96 to changeelevation relative to the workpiece 50.

In a preferred embodiment of the present invention, a.one degreerotation of the coarse adjustment

sc 216 causes a 5 μm change in elevation of the cutting tool edge 96. Anupper clamping feature 232 in the

swin arm base 48 allows for enabling and disabling of the coarseadjustment screw 216. In a preferred embodiment

one degree rotation of the fine adjustment screw 218 causes a 0.021 μm(21 nm) change in elevation of the cutting tool edge 96. A lowerclamping feature 234 in the swing arm base 48 is used to hold thedifferential screw assembly 66 in the upper portion 60 of the swing armbase.

In the present embodiment of the rotary fast tool servo, thedifferential screw assembly 66 provides a ±1.27 mm of change inelevation of the cutting tool edge 96.

Alternative embodiments of differential screw assemblies are availablethat provide other greater or lesser changes in elevation of the cuttingtool edge 96. In a preferred embodiment of the rotary fast tool servo40, the swing arm 102 is configured to couple an actuator 68 which ismounted to the upper portion 60 of the swing arm base 48 with athermally insulating spacer. The thermally insulating spacer, as shownin the next embodiments restricts the flow of heat from the actuator 68into the swing arm base 48. An enclosure, as

sho in the next embodiment, around the actuator 68 allows for thecontrolled removal of the heat generated by the

actuator during use, helping to prevent the heat from entering the restof the machine by thermal conduction, convection, and radiation.

Different methods for aligning the axis of rotation of the actuator 68to the swing arm axis of rotation are possible. One method includesprecision machining of the mounting surfaces on the interface hardwarebetween the actuator 68 and the upper portion 60 of the swing arm base48, and precise alignment of the interface hardware to the swing armaxis of rotation 46 during assembly. Another method includes using aflexible coupling to accommodate misalignment between the actuator 68and the swing arm 48. A flexible coupling is a well-known device used inthe art for transmitting torque between two bodies while accommodating amisalignment between those bodies due to relaxed manufacturing andassembly tolerances

Damping mechanisms, such as discussed with respect to the nextembodiments, can be added between the swing arm 104 and the swing armbase 48 to improve the dynamic performance of the fast tool servo. Theareas near the upper skirt 192, lower skirt 194, upper hub 110, andlower 112 are possible locations for installing damping mechanisms.

Displacement and rotation sensors, such as discussed with respect to thenext embodiments, can be added between the swing arm 102 and the swingarm base 48 to provide real-time measurement data on the location andangular orientation of the swing arm relative to the swing arm baseduring operation of the fast

t servo. The areas near the upper skirt 192, lower skirt 194, andbetween the back surface 158 of the swing arm 102 and the swing arm base48 are possible locations for installing displacement and rotationsensors. Additionally, the actuator 256 can be equipped with rotationsensors to provide real-time measurement data

the location and angular orientation of the swing arm 102 relative tothe swing arm base 48.

Referring to FIG. 18, an alternative fast tool servo system 250 is shownin accordance with a preferred embodiment of the present invention. Thefast tool servo 250 has a swing arm assembly 252, a base 254, andactuator 256. The base 254 of the fast tool servo 250 is located on arotating table 242 of the machine tool 24 such as an auxiliary spindleon a two-axis precision lathe. The rotating table 242 rotates about anaxis of rotation 244, which is not coincident with the axis of rotationof the swing arm. Depending on the radius of curvature of the workpiece,the axis of rotation of the rotating table can be located inside oroutside of the workpiece. For example, the workpiece shown in FIG. 18can have the rotating table axis pass through the center of the small,spherical workpiece. To generate a surface on the workpiece that has aradius of

curvatur larger than the diameter of that workpiece, the axis ofrotation can be located outside the workpiece. The workpiece 50 isretained by a workpiece holder 51 attached to a spindle 243 on themachine tool 240.

The base 254 has an upper portion 258 and a lower portion 260 whichoverlie and underlie, respective

the predominant portion of the swing arm assembly 252. The actuator 256is coupled to the swing arm assembly 252. The actuator 256 is mounted tothe upper portion 258 of the base 254 with a plurality of thermallyinsulated spacers 264. The thermally insulating spacers 264 restrict theflow of heat from the actuator 256 in the base 254. In addition, thefast tool servo 250 has an enclosure 266 around the actuator 256 thatallows for controlled removal of heat generated by the actuator 256during use, helping to minimize and preferably

prev the heat from entering the rest of the fast tool servo system bythermal conduction, convection, and radiation

Another view of the fast tool servo 250 on the rotating table 242 of themachine tool 240 is shown in FIG. 19 in accordance with a preferredembodiment of the present invention. As best seen in FIG. 20, thecutting tool 90 is shown engaging the workpiece 50. As in the previousenvironment, the cutting tool 90 is carried in a slot 139 (best seen inFIG. 21) in a swing arm 268 of the swing arm assembly 252. In additionsimilar to the previous embodiment, the fast tool servo 250 has an upperchip shield 270 and a lower chip

shi 272 that protect the flexure blades from being interfered with bychips or debris coming off of the workpiece during the machiningprocess.

The motion of the swing arm 268 of the swing arm assembly 252 ismeasured by a pair of sensors

28 The motion of the swing arm 268 is limited by a plurality of hardstops 278 as described hereinbefore. The sensors 280 are shown behindthe swing arm 252, and can be better seen in FIG. 20.

FIG. 20 is a view of the fast tool servo 250 without showing therotating table 242 of the machine

24 upon which it sits. The sensors 280 in this embodiment are a pair ofeddy current sensors that measure rotation of the swing arm 268 aroundits centerline 296, and translation of the swing arm in a directionperpendicular its front/back plane 302 as seen in FIG. 22. It isrecognized that the sensors 280 that determine the rotation

o the swing arm 268 can be other sensors such as, for example, but notlimited to, capacitance gauges or other types of sensors capable ofmeasuring small mechanical displacements that change at high frequency.In addition, the fast tool servo 250 has a pair of panels or sidestiffeners 282 that extend from the upper base portion 258 to the lowerportion 260 and provide for stiffening.

The actuator 256 is shown to be mounted to the upper portion 258 of thebase 254. The thermally insulating spacers 264 support and thermallyinsulate the actuator 256 from the base 254 therein restricting the flowof heat from the actuator 256 into the base 254. In addition, theactuator 256 is surrounded by the enclosure 266 that allows forcontrolled removal of heat generated by the actuator 256 during use. The

interf between the actuator 256 and the swing arm assembly 252 can beseen. The actuator 256 has an output shaft 286, as best seen in FIG. 28,which extends downwardly and is received by a clamp 288 on the swing armassembly 252, as best seen in FIG. 21.

Referring to FIG. 21, the swing arm assembly 252 has a swing arm 268that has a front face 290, a

re face 292, and a clearance cut 294. The swing arm 268 has an axis ofrotation 296 that nominally coincides

w the long axis of the swing arm 268. The swing arm 268 has an upper hub298 and a lower hub 300. The clearance cut 294 is located approximatelymidway between the upper hub 298 and the lower hub 300. The clearancecut 294 extends from the front face 290 of the swing arm 268 through theaxis of rotation and

sligh beyond. A front/back plane 302, as best seen in FIG. 22, extendsthrough the axis of rotation 296 and is

paral to the front face 290. A back clearance surface 304 of the swingarm 268 is parallel to and spaced from the front/back plane 302. Theclearance cut 294 allows the cutting tool edge 96 and a small portion ofthe cutting tool 90 to protrude from the back clearance surface 304 ofthe swing arm 268, as seen in FIG. 22, and allows workpiece to extendinto the swing arm 268 as much as possible.

As will be described in further detail hereinafter, the fast tool servosystem 250 has several mechanism for damping of motion. There is adesire to dampen the motion so that unintentional motion does not

propaga With respect to this, the fast tool servo system 250 has adamping plate 308 that is secured to the lower hub

3 of the swing arm 268. The damping plate 308 is interposed between thelower portion 260 of the base 254 an bottom plate 314. The bottom plate314 has a circular groove 318 that receives the damping plate 308.

A viscous fluid such as grease, or a viscoelastic material, isconstrained between the damping plate

3 and the lower portion 260 of the base 254 and the bottom plate 314.Rotation of the swing arm 268 causes relative motion between the dampingplate 308 and the lower portion 260 of the base 254 and the bottom

pla 314, producing a shear force in the grease or viscoelastic materialthat dissipates energy associated with

rotat of the swing arm 268.

In an alternative embodiment damping of unwanted motion between theswing arm 268 and the base is accomplished by the relative motion of anelectrically conducting plate carried by one through a magnetic fieldthat is referenced to the other resulting in eddy current losses in theplate.

As in the previous embodiments, the swing arm 268 is secured to the base254 by a plurality of flexure

blades. The lower and upper hubs 300 and 298 each have a pair of sectorsof a cylinder or pie slice shaped grooves 320 for receiving the flexureblades, as seen in FIGS. 21-24.

Referring to FIG. 22, the swing arm assembly 252 has a pair of upperflexure blades 322 and a pair

o lower flexure blades 324 secured to the swing arm 268. The pair ofupper flexure blades 322 intersect each other at a groove 336 in eachblade at a slot 326 in the upper hub as best seen in FIG. 23. The pairof lower flexure blades 324 intersect in a similar manner.

Still referring to FIG. 22, the swing arm 268 is shown with a portionbroken away. The swing arm

26 has a bore 328 for receiving a screw 330 for retaining the cuttingtool 90 as described below with reference

t FIG. 23. The center point 98 as best seen in FIG. 2C on the cuttingtool edge 96 lies nominally in the front/b

plane 302 of the swing arm 268.

Referring to FIG. 23, a back perspective view of the swing arm assembly252 is shown. The lower

pa of flexure blades 324 are positioned in the lower hub 300 by slidingthem up into a slot 332 in the lower

hub 300. The upper pair of flexure blades 322 are slid into position oneat a time into the slot 326 in the upper

hu 298 wherein the blade extending from the left front to the right rearin FIG. 23 is inserted first in position and the other blade is slidabove and slid down such that the center grooves slots 336 engage. Thecenter slots

33 are similar to that shown in FIG. 8 as related to the firstembodiment.

The swing arm assembly 252 has a tool clamp flexure 338 that has aforward arm 340 as seen in FIG.

that is biased by the screw 330 into engagement with the cutting tool90. Referring back to FIG. 23, the tool clamp flexure 338 has a back 342that is secured to the rear face 292 of the swing arm 268. The screw 330provides for biasing the forward arm 340 to secure the tool similar tothe arrangement in FIG. 7 as related to

first embodiment. In the alternative, a screw can pull the cutting tool90 in a downward direction using the lower hole.

FIG. 24 shows a front perspective view of the swing arm 268 with theupper pair of flexure blades

32 secured to the upper hub 298 and the lower pair of flexure blades 324secured to the lower hub 300. The swing arm assembly 252 has a pair ofblocks 344 associated with each of the upper hub 298 and the lower hub300 securing the respective flexure blades 322 and 324. A fastener 346extends through the block 344 through a hole 348 in the flexure bladeand into a threaded hole 349 in the hub, and a fastener 347 extendsthrough a clearance hole in the hub into a threaded hole 345 in theblock 344 as seen in FIG. 23, for securing the flexure blades 322 or 324between the block 344 and the surface of the sector groove of the hub.

The swing arm 268 has a right/left plane of symmetry 350 that containsthe swing arm axis of rotation

296 and is perpendicular to the front/back plane 302 as shown in FIG.22. The right/left plane of symmetry

3 is analogous to the right/left plane of symmetry 136 as shown in FIG.5. The slot 138, 139 in the swing arm that receives the cutting tool 90has a plane of symmetry 140 that divides the slot into a right half anda left

h portion. The slot 138, 139 is located in the swing arm 268approximately midway between the upper hub

29 and the lower hub 300. The slot plane of symmetry 140 is parallel tothe right/left plane of symmetry 350 and

offset from the swing arm axis of rotation 296 by a distance equal tothe offset radius 142. The center point

o the cutting tool (analogous to the center point 98 in FIG. 2C) is inthe plane of symmetry 140 of the slot 138,

139 and therefore offset from the swing arm right/left plane of symmetry350 by a distance equal to this offset

radius 142.

FIG. 25 is a perspective view of the base 254 of the fast tool servosystem 250. The base 254 has the upper portion 258 and the lower portion260 with a generally circular cutout 354 with additional portions cut

356 for forming an “x” shape for receiving the ends of the flexureblades 322 and 324. The “x” shape is

orien to maximize the clearance between the base 254 and the workpiece50. In a preferred embodiment the portion

cutout 356 are oriented so that the flexure blades 322 and 324 are at a45° angle from the surface-normal of

a workpiece at the point of contact between the cutting tool 90 andworkpiece 50.

A plurality of holes 358 extend from the cut-out portions 356 to theouter surfaces 360 of the upper

an lower portions 258 and 260 of the base 254 to receive a plurality oftensioning rods 362 as shown in FIG. 26. Additional holes 364 extendfrom the cut-out portion 356 to the outer surface 360 of the base 254 inorder to allow the flexure blades to be secured by a plurality ofclamping blocks 380 after being properly tensioned as seen in FIG. 27.The base has an opening 366 on a back surface 368 behind the cylindricalcut-out 354 that is used in conjunction with mounting the sensors 280.

Referring to FIG. 26, a back bottom perspective view of the swing armassembly 252 including the flexure blades 322 and 324 with one of thefour tensioning devices is shown in accordance with a preferredembodiment of the present invention. Each of the upper and lower flexureblades are placed in tension prior

t fixing the blades 322 and 324 to the base. One of the upper flexureblades 322 is shown with a pair of tensioning rods 362. Each tensioningrod 362 has a pin 370 that is received in a slot 372 in the flexureblade or 324. The tensioning rod 362 has a washer 374 and a threaded nut376 at the other end which engage the

ba 254 in pulling the ends of the flexure blades 322 away from eachother (i.e., place the blade in tension). One

the tensioning rods 362 has a spring device 378 for providing a finelycontrolled tension force on the flexure blades 322 or 324 as the nut 376is turned. Differentially adjusting the nuts 376 on a pair of tensioningrods

3 causes displacement of the swing arm axis of rotation 296, in adirection along the long axis of that pair of tensioning rods, relativeto the base 254. By differentially adjusting each of the four pairs oftensioning rods

the orientation and location of the swing arm axis of rotation 296 canbe adjusted relative to the base 254 before the outer ends of theflexure blades 322 and 324 are fixed to the base with the clampingblocks 380. The clearance hole in the flexure blade is large enough toaccommodate this adjustment without interference.

Each flexure blade 322 has a pair of clamping blocks 380 mounted to theblade that are received with the cut-out portion 356 of the base 254.These blocks 380 each receive a fastener to secure the flexure blades322 and 324 to the base 254 in tension after the swing arm axis ofrotation 296 is aligned to the base 254 and flexure blades aretensioned.

In addition, still referring to FIG. 26, the lower portion of the lowerhub 300 has a pair of attachment holes 382 below where the lower flexureblades 324 are slid into position in the slot 332. If the damping

plat 308 is attached, such as shown in FIG. 21, the damping plate 308 isattached to the lower hub 300 using these attachment holes 382.

On each side of the center portion of the swing arm 268 there aredisposed a pair of plates 384, one shown in FIG. 26, for help in dampingunwanted motion of the swing arm 268. The back 342 of the tool

clan flexure 338 is secured to the rear face 292 of the swing arm 268.In a preferred embodiment, the eddy

current sensors 280 are shown engaging the rear face 292 of the swingarm 268.

Referring to FIG. 27, the swing arm assembly 252 is positioned in thebase 254, the hubs 298 and

300 are located in their respective cylindrical cut-out 354 portion. Theclamping blocks 380 for securing the swing arm assembly 252 to the base254 are shown such that the flexure blades 322 and 324 are interposedbetween the blocks 380 and the wall of the additional cutout 356. Thetensioning rods 362 are shown extending through the hole 358 in theupper portion 258 of the base 254. The additional holes 364 are used tosecure fasteners to the clamping block 380 to retain the flexure blades322 and 324.

The sensors 280 are shown extending from the opening 366 in the base 254to the swing arm 268. The tensioning rods 262 are shown in the upperportion; similar rods are used in the lower portion but are not shown inthis figure. After the flexure blades 322 and 324 are fixed to the base254 by the clamping blocks 380, the tensioning rods 362 can be loosenedby backing off nuts 376, although it is generally not necessary to doso. The cutting tool 90 is projecting from the slot 138, 139 in theswing arm 268.

Referring to FIG. 28, the upper chip shield 270 and the lower chipshield 272 are shown secured to the base 254. The swing arm 268 has apair of annular rings or skirts 390 that interact with the shields 270and

2 as described with respect to the first embodiment.

The swing arm assembly 252 has a plurality of hard stops 392. The hardstops 392 are retained by the upper chip shield 270. The hard stops 392prevent excessive rotation of the swing arm 268 that can damage

t flexure blades 322 and 324, and work identically as described andshown in the embodiment illustrated in FIG. 14. Referring to FIG. 14, asmall gap 213 between an end of each hard stop 392 (212) and the swingarm 268 (102) allows normal rotation of the swing arm. The hard stops392 (212) act in pairs to limit the rotation angle of the swing arm 268(102) to prevent damage to the upper and lower pairs of flexure blades322 and 324. Excessive rotation of the swing arm 268 (102) causesclosure of a pair of gaps 213 that limits rotation of the swing arm.

The sensors 280 are shown in a mounting block 394 mounted to the backface or back surface 368 of base 254. The output shaft 286 of theactuator 256 is held by the clamp 288 to connect the actuator 256 to theswing arm assembly 252. It is recognized that a flexible coupling can beused between the output shaft 286

a the swing arm assembly 252 to accommodate misalignment, between theoutput shaft of the actuator and the swing arm assembly.

FIG. 29 is a side view of the fast tool servo system 250 in accordancewith a preferred embodiment

o the present invention and is a view similar to that of FIG. 20. Thecutting tool 90 is shown engaging the working piece 50 retained on theworkpiece holder 51. The upper chip shield 270 and the lower chip shield

2 protect the upper flexure blades 322 and the lower flexure blades 324,as seen in FIG. 27 from chips and

deb that are produced during machining. The sensor 280 is shown engagingthe rear face 292 of the swing arm

26 In addition, the tool clamp flexure 338 is shown secured to the swingarm.

The thermal insulating spacers 264 restrict the flow of heat from theactuator 256 into the base 254. The enclosure 266 encircles the actuator256 to allow controlled removal of heat. The side stiffeners 282 stiffenthe base 254.

In a preferred embodiment, the system for a high bandwidth rotary fasttool servo establishes the swing arm axis of rotation 296 and 46 in avertical direction. Other preferred embodiments of the system can

establ the swing arm axis of rotation 296 in a horizontal direction, orany other direction, depending on the

intende application of the fast tool servo.

In operation, the fast tool servo 250 is used in conjunction with themachine tool 240, for example, a precision lathe, as shown in FIG. 18.The spindle 243 rotates about a horizontal axis whereas the rotating tab

242 rotates about a vertical axis. In addition, one of the units movesin the cross-slide direction that is in and of the page with respect toFIG. 18 whereas the other one is capable of moving into the in-feedslide position that is in a left and right direction. The position andvelocity of the cross-slide and in-feed slide are measured within aprecision lathe controller 412. In addition, the rotation position andvelocity of the workpiece 50 and the auxiliary spindle (rotary table)242 can be measured with sensors located in the machined tool 240.

FIG. 31 shows a schematic diagram of the inter-relationship in controlof the fast tool servo system

2 with that of a precision lathe or machine tool 240. The machine tool240 with rotating table 242 such as shown in FIGS. 18, 19, or 32A-C hassensors to determine the position of the workpiece spindle 243 andtherein the workpiece 50. The spindle 243 is held by a base unit, whichis capable of moving in at least one direction. The position of the baseunit, the rotational speed and position of the workpiece spindle 243form inputs into a precision lathe controller 412. The rotating table242, on which the fast tool servo 250 is mounted, is

capable being moved in a controlled fashion in a direction perpendicularto the direction of the base unit in addition

t rotating about a vertical axis. The translational and rotationalpositions of the rotating table are likewise input into the precisionlathe controller 412. In addition to the sensors within the precisionlathe 240, the fast tqol servo 250 has a plurality of sensors 280 and406. With respect to the base 254, the position of the swing arm 268 isdetected. With sensors such as, for example, sensors 280 as shown inFIG. 29, the rotation position and translation of the swing arm 268 in adirection perpendicular to its front/back plane 118, 302 is detected.

The fast tool servo controller 402 uses feedback information via thesensor amplifiers from the sensors 280 and additional sensors 406 tocompute the position and velocity of the tool 90, and produces a commandsignal for the fast tool servo actuator 256. The command signal from thefast tool servo controller 402 to the actuator 256 is modified by asignal conditioning amplifier that uses feedback from the actuator 256,and the signal indicative of the modified command forms an input to apower amplifier that drives the actuator 256.

fast tool servo controller 402 may synthesize angular velocityinformation for the swing arm 268 from the position sensors. In analternative embodiment, a velocity sensor such as, for example, atachometer is

dispo on the actuator.

In a preferred embodiment, the fast tool servo controller 402 is themaster controller and the precision lathe controller 412 is the slavecontroller. Sensors associated with the precision lathe 240 may providefeedback information regarding the position and velocity of thecross-slide, in-feed slide, spindle, and

rotatin table to both the precision lathe controller 412 and the fasttool servo controller 402. The fast tool servo controller 402 uses theprecision lathe sensor information and the fast tool servo sensorinformation 280 and 406 to compute the spatial relationship between theworkpiece 50 and the tool 90. The fast tool servo control 402 comparesthe computed relationship between the workpiece 50 and the tool 90 tothe desired relationship between the workpiece and the tool, andgenerates commands to the precision lathe controller 402 to position

and orient the cross-slide, in-feed slide, spindle, and rotating table,and also generates commands to the fast

t servo controller to position the tool 90. The precision lathecontroller uses feedback information from the precision lathe sensors tocompute signals that are issued to the precision lathe actuators toaffect the commanded positions and orientations of the cross-slide,in-feed slide, spindle, and rotating table. The fast to

servo controller 402 uses feedback information via the sensor amplifiersfrom the sensors 280 and additional sensors 406 to compute the positionand velocity of the tool 90, and generates a command signal for the fasttool servo actuator 256. The command signal from the fast tool servocontroller 402 to the actuator 256 is modified by a signal conditioningamplifier that uses feedback from the actuator 256, and the signal

indicati of the modified command forms an input to a power amplifierthat drives the actuator 256.

In a preferred embodiment, the fast tool servo system can be a computernumeric control (CNC) machine tool system. A preferred embodiment of thepresent invention can include a programmable

compute

In an alternative embodiment the precision lathe controller 412 is themaster controller and the fast to

servo controller 402 is the slave controller. In this embodiment thefast tool servo controller 402 is responsible for local control of thetool 90 as described with respect to the previous embodiment, and theprecision lathe controller 412 is responsible for local control of theprecision lathe 240 as described hereinbefore. In this embodiment, thefast tool servo controller 402 may provide the precision lathecontroller 412 with information on the position and velocity of the tool90. The precision lathe controller 412 treats the fast tool servo system250 as an additional machine axis under its command and synchronizes theposition and velocity of the tool

9 with the position and velocity of the cross-slide, in-feed slide,spindle, and rotating table in accordance with

desired relationship between the tool 90 and workpiece 50.

In a preferred embodiment, the fast tool servo controller 402 with anactuator 256 having the

capabili of two-thousand movements per second and a range of travel of±0.14 degrees, sensors 280, and an offset radius 142 of 5 mm allows thefast tool servo 250 to develop a tool tip acceleration in excess of 25g's follow a 5 micron peak to valley sinusoidal surface with 50 nmaccuracy at 2 kHz.

The cutting edge 72 on the cutting tool 90 is spaced from the axis ofrotation 46, 296 by an offset

rad 142 as shown in FIGS. 5 and 24. Rotation of the swing arm 102, 268caused by the actuator 68 causes a controlled rapid movement of thecutting edge into and out of engagement with the workpiece as thespindle rotates therein, allowing the production of work pieces withcomplex shapes. For example, referring to FIG.

a stasphere shape having a plurality of icosahedron or multisidepolyhedron features such as, for example, depressions or dimples withsmooth or abrupt transitions between surfaces is produced by therotation of the workpiece on the spindle as the cutting edge is movedinto and out of engagement with the material while the rotating table242 carries the fast tool servo 40, 250 from the pole of the workpieceto its equator. In addition the applications of the preferredembodiments include production of lenses for telescopes or ophthalmics.

FIGS. 32B and 32C illustrate views of a precision lathe having aworkpiece 486 and a fast tool servo system in accordance with apreferred embodiment of the present invention. These figures illustrateenlarged views of the fast tool servo system, which is placed on arotary table 488, in relation to the workpiece 486, the cross-slide 452and in-feed slide 462 described hereinbefore.

FIGS. 33A and 33B are schematic diagrams of a variable reluctanceactuator in accordance with a preferred embodiment of the presentinvention. In a preferred embodiment the actuator and swing arm are anintegral unit. This embodiment includes a normal-direction variablereluctance rotary actuator for an approximately 10 kHz arid higherrotary fast tool servo system. Two pairs of actuators provide back andforth rotation of a swing arm 530 that holds a tool 522 at a locationspaced from the axis of rotation, creating a too

motion towards and away from a workpiece. In a preferred embodiment,using a flux density of approximate

1.5 Tesla, a 1000 g's of tool acceleration required to follow a 5 micronpeak to valley sinusoidal surface at, for example, 10 kHz can beachieved. This alternative preferred embodiment operates using theprinciple of

vari reluctance wherein a force is generated between two components in amagnetic circuit as it naturally

attempt reduce the overall reluctance of the magnetic circuit. In thepresent embodiment, reducing one or more of the air gaps between themovalble rotor 546 and the stator 543 reduces the reluctance of themagnetic circuit. The permanent magnets 540 and 542 provide magneticflux biasing so that the magnetic flux generated by the current (i) inthe coils 544 causes rotation of the rotor 546. For the direction of thecurrent (i) shown in FIG. 33B the magnetic flux generated by the coils544 is steered by the permanent magnets 540 and 542 from the upper leftcorner of the rotor 546 to the lower right corner of the rotor causingclockwise rotation of the

rotor Reversing the direction of the current (i) shown in FIG. 33Bcauses the magnetic flux generated by the coils to be steered by thepermanent magnets 540 and 542 from the lower left corner of the rotor546 to the upper right corner of the rotor causing counter-clockwiserotation of the rotor. A normal-direction variable

reluctar actuator is an electromagnet that closes the gap between itselfand a target. The attractive force increases with the inverse of the gapsquared and can thus provide a small stroke actuator with a high forcedensity. FIG.

3 illustrates stators having windings 544, which can be formed out ofvarious coils. A permanent magnet system

540, 542, is disposed between the stators. A rotor 546 is disposed inthe center of the permanent magnets. The system induces a force thatprovides for the back and forth rotation of the rotating swing arm 530that holds

t tool 522. The geometry of the flexures 524, 526, 528 is optimized toprovide the necessary guidance and support of the swing arm.

FIG. 34 illustrates a variable reluctance fast tool servo employing anarmature 564, tool 566, first actuator 560 and second actuator 562. Theservo may be used in a biased manner to facilitate linear operation orit may be operated in an unbiased configuration. Armature 564 may besupported on flexures or air, oil,

o on plain or rolling element bearings.

FIG. 35A illustrates a variable reluctance actuator comprising a tool566, a backside endplate 568, a

b side air gap 570, a tool side air gap 572, a tool side endplate 574,an inner magnetic shell 576, an outer

magn shell 578, a permanent magnet 580 and a tubular backbone 582. Theactuator of FIG. 35A has an axis of motion across the page (i.e., leftto right) and has the tool 566 mounted on the centerline of theactuator.

FIG. 35B illustrates an end view of the variable reluctance actuatortaken along line A-A′ showing the inner magnetic shell 576, the outermagnetic shell 578 and the direction of the magnetic flux radiating

outwa FIG. 36A illustrates the armature of FIG. 35A and shows themagnetic backside endplate 568, the magnetic tool side endplate 574, andthe non magnetic tubular backbone 582. FIG. 36A also illustrates tool

mounted along the centerline as well as showing alternative toolmounting locations 566A and 566B

proxima to the outer edges of tool side endplate 574.

FIG. 36B illustrates an exploded view of the stator of FIG. 35A. Thestator is comprised of a backside coil 584, a magnetic outer shell 578,a permanent magnet 580 for providing radial magnetization, a magneticinner shell 576 and a tool side coil 586.

FIG. 37 illustrates an embodiment where the armature and stator(optionally) can be supported on flexures and bearings, or air bearings,or fluid hydrostatic bearings to constrain motion to only axial motion.

the stator is suspended on bearings, it can serve as a reaction mass.The stator can also use air or fluid for cooling and/or clamping. Theembodiment of FIG. 37 employs two stator flexures 590 and two armatureflexures 588.

FIG. 38A illustrates a permanent magnet biased actuator employing asingle winding 587 for

produci a linear motion in the vertical plane (top to bottom in theplane of the page).

FIG. 38B illustrates an embodiment of a permanent magnet biased rotaryactuator as used in general scanning applications. The rotary actuatorof FIG. 38B comprises a magnetic left yoke 592 having a left winding, amagnetic right yoke 594 having a right winding, an armature 595, and apermanent magnet 596.

axis of rotation 598 about the center of the armature of the rotaryactuator of FIG. 38B is counter clockwise

i the plane of the page.

FIGS. 39A and 39B illustrate current biased actuator configurations. Thecurrent biased configuration can use bias current to replace permanentmagnets. Using current allows adjustable bias levels; however, itrequires more power dissipation due to the current in the coils used forbias.

FIG. 39A illustrates a current biased actuator having linear motion in avertical direction in the plane the page. The actuator comprises a firstcoil 602 and second coil 600 wound around an “H” shaped core 604.

FIG. 39B illustrates a four coil configuration of a current biasedactuator having rotary motion in a counter clockwise direction 616 inthe plane of the page. The actuator of FIG. 39B comprises a first coil608

second coil 610, a third coil 612, a fourth coil 614 and a core 606.

Linear fast tool servos are one configuration that can be used to makeophthalmic lenses, and these

h the advantage that they are easier to measure and calibrate. However,they have significant reaction forces if high accelerations are used.For example, if the tool is moved in a sinusoid of 5 μm peak-to-peakamplitude, then the motion can be described as:x(*)=2.5<10⁻⁶ sin ωt meterswhere ω is the frequency of oscillation. More generally, for apeak-to-peak amplitude of A, the motion is described by:$x{{(*}{)\quad = {\frac{A}{2}\omega^{2}{{sin\omega}t}}}}$and the peak acceleration is $\frac{A}{2}\omega^{2}$

If we choose A=25.10⁻⁶ m, and ω=2π×10⁴ (10 kHz), then we find:$\begin{matrix}{\chi_{\max} = {{{\frac{2.5 \times 10^{- 6}}{2}\left( {2{\pi \times 10^{4}}} \right)^{2}} \cong {5000\quad m\text{/}\sec^{2}}} = {500\quad{G'}s}}} & \quad\end{matrix}$

This high acceleration can result in very significant forces. Forexample, if the moving mass is 10 gm the resulting force isF=ma=0.01·5000=50N.

FIG. 40 provides an illustration showing the relationship between theseforces. Such a large force

ca shake the precision machine, which carries that fast tool servo. Thusin some cases, it will be necessary to

us balance or reaction mass to absorb these forces. By way of example, aforce F₁ is used to provide the driving force to the fast tool servo620. The majority of this force is applied to the balance mass 618,resulting in its acceleration. Thereby, the large FTS forces do not needto be applied to the machine frame 619. The force

F (termed the “drift force”) prevents the assembly from drifting out ofrange, by applying a corrective action to keep the average balance massposition at the center of travel.

Such a reaction mass configuration is shown in FIG. 37. Here F₁ is theforce on the tool servo, and the stator serves as a balance mass bymoving independently on the indicated flexures. Force F₂ is generated byany conventional means such as, for example, coils, magnets,electromagnets, and the like to control drift.

It is also possible to design analogous balance masses for rotationalfast tool servos. However, it is usually easier to have a machine frametolerate reaction torques, since the moment of inertia for a massincrement dM scales as dMR and since plates are stiffer in shear than inbending.

The movement of the tool servo can be constrained in translation (linearFTS) or in rotation (rotary FTS) by any of the bearing technologies usedin precision motion control systems. These include flexures, rollingelement bearings, air bearings, hydrostatic bearings, or magneticbearings.

It may also be desirable to introduce controlled gaps filled with air,oil, ferrofluid, or other

appropriat damping material, such as, for example, Sorbothane, etc., inorder to introduce controlled damping for the FTS

motions.

FIG. 41 illustrates a schematic diagram showing the forces applied in aFTS. In particular, FIG. 41 shows motion in a right/left direction onthe page in relation to shear damping using oil 622, shows motion in

up/down direction in relation to the page using a squeeze film damping624 and angular motion in a counter-clockwise direction in relation tothe page using oil 622 as a squeeze film in the xy plane. The magneticcore FTS's will be laminated, or made of metallic glass, or made ofsintered material in order to reduce the effects

eddy currents and thereby preserve high bandwidth.

The nonlinear effects of the variable reluctance actuators can beaddressed by some combination of the following techniques. Permanentmagnet or coil-based biasing lowers the effect of nonlinearities. The

actuat nonlinearities can be modeled and an inverse nonlinear modelimplemented in the computer control system, typically on a digitalcomputer. For example, if the actuator force varies as$F = {C\left( \frac{i}{g} \right)}^{2}$

then the calculation $i_{s} = {g\sqrt{\frac{Fd}{c}}}$results in linearity. Here F is the actuator force, I is the coilcurrent, g is the actuator gap, C is a constant, Fd

desired force in the controller, and is a current setpoint to a currentcontrolled amplifier. Flux sensing can be implemented either via the useof a flux sensor in or adjacent to the gap (Hall cell, magnetoresistive, etc.) or flux sensing coils wound on the actuator pole faces.

FIG. 42 illustrates an actuator having a coil 628, stator 626 andarmature 630 and Hall cells 631 a and 631 b. In addition, FIG. 42 showsa Hall cell further having a servo coil 632.

FIG. 43 illustrates an actuator derived from a Hall cell. The embodimentof FIG. 43 facilitates motion

about a vertical axis. Rotation may be about a first axis 629 forming avertical plane touching the tip of tool 566 or rotation may be about asecond axis passing through armature 630. The embodiment of FIG. 43comprises an armature 630, a tool 566, a lower stator 626A, having twolegs, an upper stator 626B, having

two legs, a permanent magnet biasing member 634, a lower first coil632A, a second lower coil 632B, a first upper coil 632C and a secondupper coil 632D. The permanent magnet biases the 4 legs forcing thearmature. The coils 632A-D on the legs steer the flux to create a torqueon the armature 630. Armature 630 may be

suspen on some form of bearing to constrain motion to rotation.Flexures, rolling element, air, oil hydrostatic

restrai and other means may alternatively be employed to constrainmotion.

FIG. 44A presents top view of the embodiment shown in FIG. 43, FIG. 44Bpresents a side view of the embodiment of FIG. 43 and FIG. 44C presentsa face view of the embodiment of FIG. 43.

FIGS. 45A and 45B illustrate embodiments of an actuator employing biasflux from permanent

magn to provide preload force for pressurized air or oil hydrostaticbearings 636. Oil film or air film in a bearing provides compressive andshear damping. In some situations it may not be possible to use axis #1(long

reac tool), in which case, an alternate axis can be used. FIG. 45Billustrates axis #2 being employed as the axis

o rotation.

FIGS. 46A and 46B illustrate rotational fast tool servos that can havean axis of rotation oriented either vertically (FIG. 46B) orhorizontally (FIG. 46A). FTS motion can be sensed by precision motionsensors

su as capacitive displacement probes, inductive displacement probes,optical probes, or other means. The embodiment of FIG. 46A comprises aspindle 638, post 640, and tool 566.

FIGS. 47A and 47B illustrate a radial configuration of flux-biased coilscapable of steering flux from front to back side of armature, andthereby creating axial thrust. The embodiment of FIG. 47A comprisescores 642A and 642B radially disposed around an armature 648 andemploying bias magnets 650A and 650B. In addition, the embodiment ofFIG. 47 A comprises coils 644A, 644B, and 644C, a mechanical structuralbackbone 646 and a tool 566. Motion is left/right with respect to thepage for the embodiment of FIG. 47A. FIG. 47B illustrates a back endview of the embodiment of FIG. 47A and comprises eight cores 652A-H,eight coils 654A-H and eight bias, permanent magnets 656A-H.

FIG. 48 illustrates a core having a wedge-shape, which reduces oreliminates the occurrence of back-iron saturation.

FIG. 49 illustrates a micropositioner 700 in accordance with analternative embodiment of the present invention. The micropositioner 700contains an outer movable shell, which is better illustrated by thecross-sectional side view of the micropositioner 700 shown by FIG. 50.Referring to both FIG. 49 and FIG. 50, the outer movable shell 710contains a first end cap 712, a second end cap 714, and at least onenon-magnetic strut 713 that is connected to the end caps 712, 714 sothat the end caps 712, 714 move together. The end caps 712, 714 aremagnetic. It should be noted that while FIG. 50 illustrates thenon-magnetic strut 713 being connected to side portions of the first andsecond end cap 712, 714, other configurations may be provided, such as,but not limited to, the non-magnetic strut 713 connecting to a bottom ofthe first end cap 712 and a top of the second end cap 714.

The micropositioner 700 also contains at least one securing device 800for allowing the micropositioner 700 to be secured to a structure, whilethe outer movable shell 710 is capable of moving in a positive ornegative X-axis. The securing device 800 is removably connected to anouter magnetic pole-piece 720, as well as the structure to which themicropositioner 700 is secured.

A magnetic element is located within the micropositioner 700, containingthe outer magnetic pole-piece 720 and an inner magnetic pole-piece 722located within the outer magnetic pole-piece 720. At least one permanentmagnet 724 is located between the inner magnetic pole-piece 722 and theouter magnetic pole-piece 720. It should be noted that in accordancewith the alternative embodiment of FIG. 49 and FIG. 50, one permanentmagnet is provided.

At least one coil is located between the outer magnetic pole-piece 720and the inner magnetic pole-piece 722. FIG. 50 illustrates the exampleof two coils 726, 728 being located between the outer magneticpole-piece 720 and the inner magnetic pole piece 722, where thepermanent magnet 724 is located between the coils 726, 728. In FIG. 50the coils 726, 728 are illustrated as having a positive current goinginto the page at the “X” and coming out of the page at the black dot.

The magnetic properties of the end caps 712, 714, the inner magneticpole-piece 722, and the outer magnetic pole-piece 720 may be provided,for example, by their being fabricated from powdered metal material, asolid magnetic material, or laminated with a magnetic material. Examplesof magnetic materials may include, but are not limited to, steel,silicon steel, cobalt steel, nickel iron, stainless steel, and manyother materials. One having ordinary skill in the art would knowexamples of other magnetic materials that may be used.

FIG. 51 is a schematic diagram illustrating coil and magnetic flux pathsof the micropositioner 700. One feature of the micropositioner 700 isthat a force is applied that is linear in coil current and stage (outermovable shell) displacement. As shown by FIG. 51, the permanent magnet724 provides biasing flux (shown as solid arrow lines) to upper andlower air gaps 732, 734. The permanent magnet 724 biasing flux isindependent of coil current and essentially is a linear function ofposition due to the length of the permanent magnet 724 being much largerthan the length of the air gaps 732, 734. Superimposed upon the biasingflux is a coil flux (shown as dotted arrow lines). The biasing and coilfluxes are shown as being in the same direction in the lower air gap 734and being in opposite directions in the upper air gap 732. Therefore,the net force on the outer movable shell 710 is then the difference ofthe two magnetic forces caused by the magnetic fluxes and is linear incoil current and outer movable shell 710 displacement, while thepermanent magnet 724 is much longer than the air gaps 732, 734.

Returning to FIG. 50, the outer movable shell 710 is connected to theouter magnetic pole-piece 720 via at least one rubber bearing 740. FIG.52 better illustrates positioning of rubber bearings 740 within themicropositioner 700. In accordance with the present exemplary embodimentof the invention, the micropositioner 700 contains four rubber bearings740 in the form of sheets. The use of rubber bearings between the outermovable shell 710 and the outer magnetic pole-piece 720 provides guidedmotion without the disadvantages of friction, stiction, and vibration ofrolling or sliding bearing systems.

Rubber bearings provide the capability of providing a compact package,while constraining five degrees of freedom. FIG. 53 is a schematicdiagram further illustrating positioning of rubber bearings 740 anddegrees of freedom. The unconstrained degree of freedom for a rubberbearing 740 is the motion parallel to the plane of the rubber bearing740. As a result, the micropositioner 700 has one degree of freedom,which is in the x-axis. In FIG. 53, the four rubber bearings 740 arenumbered 1, 2, 3, and 4.

It should be noted that stainless steels often present adhesive problemsdue to low surface energy. As a result, use of a primer coating would bean appropriate method to increase bond strength. Another method thatimproves adhesion, and that is beneficial on stainless steels tomaximize corrosion resistance, is passivation. Passivation is a processby which a uniform protective oxide film is created on the exposedsurfaces of stainless steels and all containments are removed from thesurface. Passivation is beneficial if performed on micropositionercomponents prior to application of a primer coat in commercialapplications of cast rubber bearings.

In accordance with an alternative embodiment of the invention, therubber bearings may be provided as o-ring bearings. FIG. 54A and FIG.54B are cross-sectional side views of an alternative micropositioner 750where an outer movable shell 752 is suspended on a series of stackedo-rings 754 with bulging interference (FIG. 54A) and without bulginginterference (FIG. 54B).

The following provides an example of a method that may be used to obtainthe o-ring bearings. An initial step in preparing to design themicropositioner 750 is to consider the methods available forconstructing the rubber bearing. One method, as shown by FIG. 54A andFIG. 54B is to stack standard and readily available o-rings one on topof another around a square or circular post. The stacked o-rings providesufficient constraint stiffness in the radial direction to be practicalin a micropositioner.

Two cases of particular interest are the o-rings on a round post and theo-rings on a square post suspending the outer movable shell on aninverse post geometry. FIG. 54A shows an o-ring spacing scheme that willhave a stiffness that approaches that of a solid sheet when the spacingis less than an o-ring thickness, due to the constraint each bulgingo-ring will place on the others. This interfering configuration isreferred to as having bulging interference. The two stiffness limits ofthe bulging interference configuration are the continuous sheetstiffness and the stiffness of n single o-rings with no bulginginterference, where n is the number of o-rings in the stack. When theo-rings are very tightly spaced the o-ring stack stiffness willapproximate a continuous rubber sheet. Large spacing between theo-rings, such as that illustrated by FIG. 54B, will eliminate thestiffening effect of the bulging interference and the stiffness will bethat of n single o-rings.

The rubber bearings may be provided by many different processes. Whilethe exemplary embodiment of FIG. 50 contains sheet rubber bearings thatare fabricated using a standard rubber processing method, and which arelater glued in place, in accordance with an alternative embodiment ofthe invention, the rubber bearings may be cast in place.

The casting process involves creating a mold that will restrain liquidrubber in a desired shape until after vulcanization occurs.Vulcanization of the liquid rubber can be initiated in a number of ways.The primary goal of the casting process is to create a rubber sheet thatis firmly adhered to the outer magnetic pole-piece 720 and that isdevoid of any air bubbles. Accomplishing this goal requires priming theouter magnetic pole-piece 720 to promote adhesion, removing trapped airbubbles from the liquid rubber mixture, and filling the mold completely.

A beginning step in preparing the outer magnetic pole-piece 720 foradhesion may be to abrasively clean the outer magnetic pole-piece 720with sandpaper to remove any rust or other adhered contaminates. Next,dust, machine oil, and any other contaminates are rinsed away.Optionally, a solution such as, but not limited to, rubbing alcohol, maybe used to prepare the outer magnetic pole-piece 720 surfaces forapplication of a thin layer of adhesion promoter for use with liquidsilicon rubbers. Preferably, the layer adhesion promoter extends wellbeyond the edge of the rubber bearing.

The removal of air and complete mold filling may be accomplished throughthe use of a vacuum pump and bell jar. A liquid rubber reservoir may beplaced under the bell jar with the necessary plumbing for filling themold in place. The bell jar and mold may then be evacuatedsimultaneously to, for example, but not limited to, 25″ Hg belowatmospheric, which allows most air trapped in the liquid rubber toescape. Atmospheric pressure is then slowly allowed to fill the belljar, although the mold and buffer are still evacuated.

Liquid rubber is then forced by air pressure to flow from the reservoirto the bottom of the mold. In order to assure filing of the mold, therubber is allowed to continue flowing until it slightly fills a buffercontainer. The vacuum on the mold side of the reservoir is then replacedby atmospheric pressure. The buffer ensures that the mold remains filledafter the vacuum is removed and as the rubber expands while vacuum isapplied. With air pressure applied, voids in the mold are collapsed. Therubber vulcanizes under atmospheric pressure for a period of time, suchas, but not limited to, twenty-four (24) hours before the mold isopened.

While the abovementioned refers to the use of rubber bearings, there areseveral situations where metal flexures are better suited as apositioning system. Examples include, but are not limited to, inelevated or ultra-low temperatures and rubber unfriendly environments(e.g., ozone, high oxygen environments, and strong oxidizers). FIG. 55is a schematic diagram illustrating an example of the use of metalflexures 760 instead of rubber bearings 740. In addition, FIGS. 56A and56B are schematic diagrams further illustrating a metal flexure 760before (FIG. 56A) and after (FIG. 56B) flexure.

Referring to FIG. 55, FIG. 56A, and FIG. 56B, each non-magnetic strut713 is connected to the outer magnetic pole-piece 720 by at least onemetal flexure 760, two of which are shown connecting to one non-magneticstrut 713 in FIG. 55. In accordance with this exemplary embodiment ofthe invention, a metal flexure 760 is secured to the outer magneticpole-piece 720 via a bolt 762 that traverses through an opening in themetal flexure 760. It should be noted that, as shown in FIG. 55, it isideal to use two metal flexures 760 to secure each non-magnetic strut713 to the outer magnetic pole-piece 720, where the metal flexures arehorizontally opposite. One having ordinary skill in the art wouldappreciate that alternative metal flexure structural orientations may beprovided to movably connect a non-magnetic strut 713 to the outermovable shell 710.

In accordance with one exemplary embodiment of the invention, integralcapacitive position sensing devices may be used to determine position ofthe outer movable shell 710. As is shown by FIG. 57, the micropositioner700 contains a first integral capacitive position sensing device 802 anda second integral capacitive position sensing device 804. It should benoted, however, that a single sensing device may be used. Each sensingdevice 802, 804 may be provided on a printed circuit board, ceramic, orother material, and contains an electrode 805 that is capable ofdetermining a capacitance between an end cap 712, 714 and the electrode805 of the position sensing device 802, 804. Preferably, the firstposition sensing device 802 is located above a top portion of the firstcoil 726 and the second position sensing device 804 is located below abottom portion of the second coil 728. The position sensing device alsocontains a a guard 803 located between the electrode 805 and a ground807.

A change in capacitance between the first and second position sensingdevices 802, 804 provides the distance between the position sensingdevice 802, 804 and the end cap 712, 714. Circuitry (not shown) forprocessing the change in capacitance between the position sensingdevices 802, 804 may be provided on the micropositioner 700 or it may beprovided separate from the micropositioner 700, but in electroniccommunication with the micropositioner 700.

As is shown by FIG. 57, the position sensing devices 802, 804 may beshaped similar to the coils 726, 728 so that the position sensingdevices 802, 804 will fit around the inner magnetic pole-piece 722. Itshould be noted, however, that the position sensing devices 802, 804 maybe shaped differently.

One having ordinary skill in the art would appreciate that otherposition measuring devices, such as, but not limited to, a laserinterferometer, a glass scale encoder, and eddy current variablereluctance position sensors may be used for determining position of endcaps. If using glass scale encoders, two glass scales could beintegrated into the micropositioner 700 on opposite sides, and readheads may be located external to the micropositioner 700 to measure theposition differential from one side of the micropositioner 700 to theother. Such a configuration can be used to evaluate stiffness of theouter movable shell 710 and to detect parasitic motions.

Alternative micropositioner configurations may be provided in accordancewith the present invention, where the different configurations mayprovide different degrees of freedom. FIG. 58 is a cross-sectional sideview of a micropositioner 850 having two degrees of freedom, namely, theX-axis and the Y-axis. Referring to FIG. 58, a center stage 852 issuspended on a rubber bearing sheet 854. Unfortunately, actuatornonlinearities of the micropositioner 850 are higher as the force withinthe actuator is dependent on both x and y stage positions. In addition,torsional stage stiffness is close to translational stiffness, meaningthat torsion is unconstrained.

The micropositioner 860 configuration illustrated by FIG. 59 increasesthe translational torsional stiffness ratio by introducing a void, orlack of a rubber bearing sheet 862, near the center of the center stage852. Specifically, the rubber bearing sheet 862 of FIG. 59 may be in theshape of a donut. The advantage of this configuration is that thetorsional stiffness can now be designed independent of translationalstiffness. The micropositioners of FIG. 58 and FIG. 59 contain an outermagnetic pole-piece 870 and the center stage 852, where the center stageacts as an inner magnetic pole-piece. The micropositioner 860 alsocontains the rubber bearing sheet 862. A permanent magnet 876 is locatedbeneath the inner magnetic pole-piece 852 and is connected to the rubberbearing sheet 854, 862. At least one coil 878 is positioned between aside portion of the permanent magnet 876 and an internal side portion ofthe outer magnetic pole-piece 870. In addition to the abovementioned, anonmagnetic strut 880 is positioned above the at least one coil 878 andthe rubber bearing sheet 854, 862. Similar to the at least one coil 878,the nonmagnetic strut 880 is positioned between a side portion of thepermanent magnet 876 and an internal side portion of the outer magneticpole-piece 870.

FIG. 60 provides a top view of the micropositioners of FIG. 58 and FIG.59. As is shown by FIG. 60, the center stage 852 is positioned centralto the micropositioner 850. As mentioned above, the micropositionerconfiguration of FIG. 58 has two degrees of freedom, namely, the X-axisand the Y-axis.

FIG. 61 is a cross-sectional side view of a micropositioner 900 inaccordance with another alternative embodiment of the invention. Themicropositioner 900 of FIG. 61 is an ideal configuration for activevibration cancellation. The configuration is torsionally compliant andthe rubber bearing portion is composed of a stack of o-rings 902. Asshown by FIG. 61, the micropositioner 900 contains an inner magneticpole-piece 904 and an outer magnetic pole-piece 906, where a permanentmagnet 908 is positioned between a first coil 910 and a second coil 912.A movable portion 920 of the micropositioner 900 contains a first endcap 928 and a second end cap 930 connected to each other via a centralnon-magnetic strut 926 that is positioned within the inner magneticpole-piece 904. The central non-magnetic strut 926 is separated from theinner magnetic pole-piece 904 by the stack of o-rings 902.

As shown by FIG. 61, the movable portion 920 of the micropositioner 900is prevented from contacting top and bottom potions of the inner andouter magnetic pole pieces 904, 906 via a series of o-ring arrays 922.The series of o-ring arrays 922 provide for maintaining of an upper airgap 932 and a lower air gap 934. It should be noted that themicropositioner 900 configuration of FIG. 61 provides for one degree offreedom, which is in the X-axis.

Alternative micropositioner configurations may be provided wheremultiple inner or outer pole-pieces may be provided. As an example, FIG.62 is a side cross-sectional diagram of magnetic portions within themicropositioner of FIG. 63. Referring to both FIG. 62 and FIG. 63, themicropositioner 940 contains an outer magnetic pole-piece 942 and afirst and second inner magnetic pole-piece 944, 946. Similar to othermicropositioner configurations, a permanent magnet 950 is positionedbetween a first coil 952 and a second coil 954. A movable portion 960 ofthe micropositioner 940 contains a first end cap 962 and a second endcap 964 connected to each other via at least one non-magnetic strut 966.Rubber bearing sheets 968 separate the outer magnetic pole-piece 942from the non-magnetic strut 966.

As is shown by FIG. 62, there are two magnetic arrays 970, 972, whereineach magnetic array contains a first coil 952, a permanent magnet 950,and a second coil 954. The micropositioner configuration of FIG. 62provides multiple degrees of freedom.

Another alternative embodiment of the invention having multiple polepieces is illustrated by FIG. 64 and FIG. 65. FIG. 64 is a sidecross-sectional diagram of magnetic portions within the micropositioner1000 of FIG. 65. The micropositioner 1000 contains multiple magneticpole-pieces in the form of a stack of magnetic pole pieces. Referring toFIG. 64 and FIG. 65, the micropositioner contains an first magneticpole-piece 1002, a second magnetic pole-piece 1004, a third magneticpole-piece 1006, a fourth magnetic pole-piece 1008, and a fifth magneticpole-piece 1010. A first permanent magnet 1012 is positioned between afirst coil 1014 and a second coil 1016, where the first permanent magnet1012, the first coil 1014, and the second coil 1016 surround the secondmagnetic pole-piece 1004. In addition, a second permanent magnet 1018 ispositioned between a third coil 1020 and a fourth coil 1022, where thesecond permanent magnet 1018, the third coil 1020, and the fourth coil1022 surround the fourth magnetic pole-piece 1008. Of course, otherconfigurations of stacked magnetic pole-pieces may be provided, and areintended to be covered by the present invention.

A movable portion 1030 of the micropositioner 1000 contains a first endcap 1032 and a second end cap 1034 connected to each other via at leastone non-magnetic strut 1036. A first rubber bearing sheet 1038 separatesthe fifth magnetic pole-piece 1010 from the non-magnetic strut 1036,while a second rubber bearing sheet (not shown) separates the firstmagnetic pole-piece 1002 from the non-magnetic strut 1036. It should benoted that the micropositioner configuration of FIG. 65 providesmultiple degrees of freedom.

A system may also be provided having multiple micropositioners. A systemcontaining multiple micropositioners contains multiple degrees offreedom, where the degrees of freedom depend on the configuration of themicropositioners. FIG. 66 and FIG. 67 provide two examples of a systemcontaining multiple micropositioners.

FIG. 66 is a schematic diagram illustrating a system 1100 having fourmicropositioners 1110, 1120, 1130, 1140. The cross configuration of thesystem 1100 and location of the micropositioners 1110, 1120, 1130, 1140,provides three degrees of freedom, namely, in the X-axis, the Y-axis,and rotation about the Z-axis.

FIG. 67 is a schematic diagram illustrating another system 1200 havingmultiple micropositioners. As is shown by FIG. 67, the system 1200contains four micropositioners 1210, 1220, 1230, 1240 that areconfigured in a slot formation. The slot configuration of the system1200 and location of the micropositioners 1210, 1220, 1230, 1240,provides three degrees of freedom, namely, in the Z-axis, rotation aboutthe Y-axis, and rotation about the X-axis.

While the abovementioned provides two examples of systems havingmultiple micropositioner, resulting in multiple degrees of freedom, onehaving ordinary skill in the art would appreciate that there are manyother configurations possible having multiple degrees of freedom. Allsuch multiple micropositioner configurations are intended to be includedwithin the present disclosure.

It should be emphasized that the above-described embodiments of thepresent invention are merely possible examples of implementations,merely set forth for a clear understanding of the principles of theinvention. Many variations and modifications may be made to theabove-described embodiments of the invention without departingsubstantially from the spirit and principles of the invention. All suchmodifications and variations are intended to be included herein withinthe scope of this disclosure and the present invention and protected bythe following claims.

1. A micropositioner, comprising: an outer magnetic pole-piece; an innermagnetic pole-piece at least partially located within said outermagnetic pole piece; at least one permanent magnet located between saidinner magnetic pole piece and said outer magnetic pole-piece; at leastone coil located between said inner magnetic pole-piece and said outermagnetic pole-piece, wherein said at least one coil is capable ofdirecting magnetic flux between said inner magnetic pole-piece and saidouter magnetic pole-piece; and a movable shell, movably connected tosaid outer magnetic pole-piece.
 2. The micropositioner of claim 1,wherein said movable shell is movably connected to said outer magneticpole-piece via at least one rubber bearing.
 3. The micropositioner ofclaim 2, further comprising a first coil and a second coil, wherein saidpermanent magnet is located between said first coil and said secondcoil.
 4. The micropositioner of claim 2, wherein said micropositionerhas two degrees of freedom.
 5. The micropositioner of claim 1, whereinsaid movable shell further comprises, a first end cap; a second end cap;and at least one non-magnetic strut connecting said first end cap tosaid second end cap.
 6. The micropositioner of claim 5, wherein said atleast one non-magnetic strut is located within said inner magneticpole-piece.
 7. The micropositioner of claim 6, where a top portion ofsaid non-magnetic strut is connected to a bottom central portion of saidfirst end cap, and wherein a bottom portion of said non-magnetic strutis connected to a top central portion of said second end cap.
 8. Themicropositioner of claim 7, wherein a side portion of said non-magneticstrut is separated from said inner magnetic pole-piece by at least onestack of o-rings
 9. The micropositioner of claim 5, wherein said movableshell is movably connected to said outer magnetic pole-piece via atleast one rubber bearing, and wherein said at least one non-magneticstrut is connected to said at least one rubber bearing.
 10. Themicropositioner of claim 1, wherein said movable shell is movablyconnected to said outer magnetic pole-piece via at least one metalflexure.
 11. The micropositioner of claim 1, wherein said at least onepermanent magnet is located between a first coil and a second coil. 12.The micropositioner of claim 1, further comprising a position sensorcapable of determining a distance between said position sensor and aportion of said movable shell.
 13. The micropositioner of claim 12,wherein said movable shell further comprises, a first end cap; a secondend cap; and at least one non-magnetic strut connecting said first endcap to said second end cap, and wherein said position sensor is capableof determining a distance between said position sensor and said firstend cap.
 14. The micropositioner of claim 12, further comprising asecond position sensor, wherein said second position sensor is capableof determining a distance between said second position sensor and saidsecond end cap.
 15. The micropositioner of claim 12, wherein saidposition sensor is selected from the group consisting of a capacitiveposition sensor, a laser interferometer, a glass scale encoder, and aneddy variable reluctance position sensor.
 16. The micropositioner ofclaim 1, further comprising a securing device connected to said outermagnetic pole piece for allowing said micropositioner to be secured to asurface, while still allowing said movable shell to move.
 17. Themicropositioner of claim 1, wherein more than one of saidmicropositioner is provided within a system, thereby providing saidsystem with more than two degrees of freedom.
 18. The micropositioner ofclaim 1, further comprising multiple inner magnetic pole-pieces.
 19. Amicropositioner, comprising: an outer magnetic pole-piece; an innermagnetic pole-piece at least partially located within said outermagnetic pole piece; at least one permanent magnet located between saidinner magnetic pole piece and said outer magnetic pole-piece; at leastone coil located between said inner magnetic pole-piece and said outermagnetic pole-piece, wherein said at least one coil is capable ofdirecting magnetic flux between said inner magnetic pole-piece and saidouter magnetic pole-piece; and a bearing located between said permanentmagnet and said inner magnetic pole piece.
 20. A micropositioner,comprising: a series of magnetic pole-pieces; a series of permanentmagnets, wherein each permanent magnet is located between a firstmagnetic pole-piece and a second magnetic pole-piece; a series of firstcoils and a series of second coils, wherein each permanent magnet islocated between one of said first coils and one of said second coils;and a movable shell, movably connected to at least one of said magneticpole pieces.
 21. The micropositioner of claim 20, wherein said movableshell contains more than one degree of freedom.
 22. The micropositionerof claim 20, wherein said movable shell is movably connected to said atleast one of said magnetic pole pieces via at least one rubber bearing.23. The micropositioner of claim 20, wherein said movable shell furthercomprises, a first end cap; a second end cap; and at least onenon-magnetic strut connecting said first end cap to said second end cap.24. The micropositioner of claim 20, wherein said movable shell ismovably connected to said at least one of said magnetic pole pieces viaat least one metal flexure.
 25. The micropositioner of claim 20, furthercomprising a position sensor capable of determining a distance betweensaid position sensor and a portion of said movable shell.
 26. Themicropositioner of claim 20, wherein said position sensor is selectedfrom the group consisting of a capacitive position sensor, a laserinterferometer, a glass scale encoder, and an eddy variable reluctanceposition sensor.